The present invention relates generally to computerized tomography (CT) communication, and more specifically to an optical communication system employed in a CT system.
CT systems typically employ a rotating frame or gantry to obtain multiple x-ray images, or views, at various rotational angles. Each set of images is identified as a xe2x80x9cslice.xe2x80x9d A patient or object is generally positioned in a central opening on the rotating frame, typically on a table. The table is axially movable within the central opening so that the patient may be positioned at various locations enabling respective slices to be obtained at multiple axial positions. Each of the slices obtained is then processed in a computer to produce enhanced images that are useful for diagnoses and inspection.
The rotating frame typically includes an x-ray source, a detector array and electronics necessary to generate image data for each view. An electronics system, typically stationary, is employed to process raw image data. It is thus necessary to communicate image data between the rotating frame and the electronic system for image processing.
The rate of data communication between the stationary electronic system and the gantry is important because the rate affects the speed at which the images can be processed. It is desirable to obtain image views as fast as possible to maximize image quality, reduce patient discomfort, and to maximize equipment utilization. In current CT systems, a single view typically comprises about 800 detector channels with a 16 bit representation for each individual detector channel and is typically repeated one thousand times per second, yielding a net data rate of about 13 million bits per second (Mbit/sec) for image data. Advanced CT systems capable of simultaneously constructing multiple image slices by employing four, eight, sixteen, or more times as many detector channels, will increase the required data rate to the hundreds of mega-bits per second range.
Prior CT systems have employed brushes, slip rings, and radio frequency links for communicating the image data between the rotating frame and the stationary frame. CT systems utilizing brushes and slip rings for communications have generally suffered significant limitations in data transfer rates due to the substantial time required to propagate the signals around the circular slip rings. At the desired data rates, the electrical path length around the rings is an appreciable fraction of the data bit transfer period so that electromagnetic waves propagating around the rings in the opposite direction may arrive at the reception point at substantially different times within the bit transfer period causing signal interference.
Additionally, radio frequency communication links, historically, have not been able to achieve the very high data transfer rates required of future CT systems at reasonable costs. Radio frequency links typically are more expensive to produce as the data rate increases because of the electromagnetic emissions requirements that must be met. As such, it is desirable to employ a CT communications link between the stationary electronics and rotating electronics that can operate with very high data rates without causing interference with other equipment.
It is also desirable to provide a communication link between the stationary frame and the rotating frame that is immune to electromagnetic radiation interference such as is typically produced in a hospital environment by cellular telephones, defibrillating devices, surgical saws, and electrical noise produced by any given CT system.
Current optical rotary links are expensive. One type uses lenses, mirrors, or many emitters and detectors to insure continuous optical communication at any gantry angle. Such systems require expensive alignment. Another type of rotary link uses an xe2x80x9coptical brushxe2x80x9d that contacts an optical transmission line with sufficient force to deform the line. At the deformity the high data rate optical data signal can enter (or exit) the line at such an angle as to be captured within the transmission line (total internal reflection) and then propagate, unimpeded, to a detector disposed at the end of the transmission line. This then provides a mechanism for coupling an externally generated high data rate optical data signal into the line at any point along the transmission line (at any gantry angle). The deformation point, however, moves along the transmission line as the gantry rotates and this process eventually causes the transmission line and coupler to wear, resulting in failure.
Yet another type of rotary optical link uses a transmission line that is doped with a dye that becomes temporarily luminescent when irradiated with laser light. The luminescent radiation is from inside the optical transmission line and a portion of this optical data signal is at such an angle as to be captured within the transmission line. Existing dyes have a response that is too slow to support the desired high data rate. Furthermore, the dyes eventually degrade.
Finally, another type of rotary link uses an optical transmission line, for example, a fiber that is heat treated to create many small fractures. Each fracture scatters high data rate optical data signal at such an angle as to be captured within the line. With this approach, the treated fiber is very small and brittle, and the coupling and propagation losses are high. In many of the above approaches, there is a dead spot or gantry angle where communication is not supported.
Accordingly, there is a need in the art for an improved communications link for CT x-ray machines.
A computed tomography system employs an optical communications link to reliably transmit high data rate data. The communications link comprises an optical emitter, an optical transmission line comprising at least two sections, a plurality of optical deflectors disposed randomly within the transmission line, and an optical receiver. The optical emitter is attached to the gantry of the computed tomography system and extends along the length of the gantry. The optical emitter generates a high data rate optical data signal, which travels along the optical transmission line in correspondence with data generated by detector array on the gantry. The plurality of optical deflectors causes portions the high data rate optical data signal to be internally reflected and subsequently refracted from the transmission line. The optical receiver disposed near the transmission line detects the portion of high data rate data refracted from the transmission line.